Furnace assembly for thermal analysis use

ABSTRACT

This invention relates to an enclosed heating furnace assembly which is adapted to be coupled to and become a part of a mass spectrometer adjacent to the ion source (usually) within the instrument. The furnace includes a heating device usually utilizing a helical coil and reflective surface and is adapted to be temperature controlled by means of temperature-sensing means disposed within a separate thermal analysis cell which is adapted to be disposed within the furnace. Means are provided for evacuating the interior of the furnace enclosure and for introducing gas or vapor to the furnace enclosure. Means are also provided for apertures of various sizes to open from the furnace enclosure to the mass spectrometer.

United States Patent Inventors Appl. No. Filed Patented Assignee Horst G. Langer Wayland;

Earl D. Ayers, Auburn, both of Mich.

Sept. 9, 1969 Dec. 28, 1971 The Dow Chemical Company Midland, Mich.

FURNACE ASSEMBLY FOR THERMAL ANALYSIS USE 5 Claims, 3 Drawing Figs.

U.S. Cl 13/31, 250/41.9

Int. Cl H05!) 3/26 Field of Search 13/22, 25,

References Cited UNITED STATES PATENTS 3,414,661. 12/1968 Reed 13/25 X 3,431,451 3/1969 Brunnee et a] 250/41.9 S X Primary Examiner-Bernard Gilheany Assistant Examiner Roy N. Envall, Jr. Attorneys-Griswold and Burdick and Earl D. Ayers ABSTRACT: This invention relates to an enclosed heating furnace assembly which is adapted to be coupled to and become a part of a mass spectrometer adjacent to the ion source (usually) within the instrument. The furnace includes a heating device usually utilizing a helical coil and reflective sur- Mass spec/rome/er- /on source 102 F 74 3 58b I V 1 10 Z -76 -68a I1 16 20 '5 Vacuum 66 18 v 18 5 FURNACE ASSEMBLY FOR THERMAL ANALYSIS USE BACKGROUND OF THElNVENTlON This invention relates to furnace assemblies adapted to receive a thermal analysis cell and particularly to furnace assemblies which are adapted for use in a mass spectrometer.

Accordingly, a principal object of this invention is to provide an improved thermal analysis cell receiving and heating assembly for use under high-vacuum conditions.

Another object of this invention is to provide an improved radiant heating furnace and thermal analysis cell-receiving assembly for use under high-vacuum conditions in a mass spectrometer.

A further object of this invention is to provide-a furnace assembly wherein means are provided to meter gaseous thermal reaction products into a mass spectrometer.

Still another object of this invention is to provide a furnace assembly in which reactive or carrier gases and/or vapors may be applied to sample material in a cell inserted in thefurnace.

Mass spectrometers are sometimes equipped with devices which allow the heating of samples within the confinement of the mass spectrometer vacuum or within'the ion source, and such devices sometimes also allow the measurementof sample temperatures during the heating process and are used in the operation known as thermal analysis. A problem arises in' the use of such devices, however, because some samples emit a great volume of gases and thus overburden the vacuum system of the mass spectrometer.- Further, in many instances it would be advisable to insert a reactant gas or vapor adjacent to the sample material, and this procedure is not practical with the prior art devices.

ln accordance with this invention, there is provided an enclosed furnace assembly which is cylindrical in overallconfiguration and is supported by a valved tubular thermal analysis cell input and sealing assembly.

The furnace has internal structure defining, in effect, an axial concentric bore with, usually, a reflective inner surface extending therethrough whichis concentrically aligned with the cell input and sealing assembly. The furnace has, for example, an array of axially disposed support rods within said bore, the array being dimensioned to fit around an inserted cell assembly. A wire heating filament is wrapped-around the support rods, with the leads from the filament passing through the metal disc and adapted to be coupled to a controlled energization source (not shown).

The top of the furnace assembly has a larger aperture therein and mechanically driven. opening and closure means covering the aperture. Means are provided for evacuating the furnace enclosure and/or for introducing gas or vaportothe furnace enclosure.

The assembly is inserted into a mass spectrometer adjacent to the ion source.

The invention, as well as additional'objects and advantages thereof will best be understood when the following, detailed description is read in connection with the accompanying drawing, in which: 7

FIG. 1 is a diagrammatical view showing apparatus in,ac-, cordance with this invention coupled to a mass spectrometer, and

H0. 2 is a side elevational view,-partly in section, of a furnace and cell probe insertion .and sealing assembly in accordance with this invention, and

FIG. 3 is a sectional view taken along the line 3-3 of FIG.

Referring to the drawing, and particularly to H6. 1, there is shown a mass spectrometer 12 having a tubular member 14 extending perpendicularly therefrom. An additional tubular element 42 having a compression coupling 44 at its outer. end and having a ball-type vacuum sealing valve 40 coupled thereto is coupled to the outer end of the member 14. A cell probe assembly 46 (see FIG. 2) is shown partly inserted into the entry and sealing assembly. A diffusion pump 52 is coupled by means of valve 54 and tube 56 to a forepump 58and by means of a tube 60 and valve 62 to the mass spectrometer 12. The tubular element 42 is coupled through tube 48 and valve 50 to the tube 56 between the valve 54 and the forepump 58. Side tubes 108, I00 extend from the tube 14 for evacuating a furnace assembly (not shown) disposed therein orfor introducing gases or vapors.

Referring now to FIG. 2, as well as to FlG. 1, there is shown the mass spectrometer tube 12 having a tubular member 14 extending transversely therefrom adjacent to the ion source 22 of the mass spectrometer. The member 14 has an outwardly extending flange 16 at its outer end. A metal plate 18 on which is supported the furnace an cell probe entry and sealing assembly 10 is sealed, as by the fillet 20, for example, to the flange 16. A threaded tube 68 extends. transversely through the plate 18 generally in coaxial relationship with the member 14. A tubular element 42 containing a so-called vacuum ball valve 40 is coupled to the tube 68 by means of coupling 66. A seal nut element 64 seals the tube 68 and element-42 (and coupling 66) against the plate 18 through which the tube 68 passes.

A coupling 30 having a flange element 28 welded thereto as at 28, is threadedly and hermetically coupled to the end of the tube 68 which lies within the tubular member 14.

I 'An annular sleeve 94 having a heat-reflective inner surface 76, usually a'coating, thereon, surrounds and is supported from and sealed to the flange element 28.

An annular plate 74, usually made of metal and at least approximately of the same outer dimension as the diameter of the flange 28, is disposed parallel to the flange 28 and is hermetically sealed thereto by screws 36, for example.

An array of electrically insulating support rods 38a, 38b,

and 38c are disposed between the annular plate 74 and flange set to be aligned with the sample container in the cell inserted in the furnace assembly).

A metal-enclosed, variable-aperture devicel02 is coupled to the plate 74 over the aperture 110. The variable-aperture device 102 may contain an iris-type element generally of the type used in. cameras which opens and closes in response to movement of a rim element, the rim element being driven by a worm element powered by a small electric motor within the device 102. v

' Other variable-aperture devices include a rim-driven rotating plate having apertures of various sizes therethrough in an array in which a fixed amount of-movement of the rim moves anotheraperture in alignment with the aperture 110.

A third variable-aperture device is a rim-driven circular plate having a slot which varies in width running around it and so aligned that part of the slot is aligned with the aperture 110. Thus, movement of the rim of the plate will change the effective opening for gas to pass through aperture 110 and thence into the mass spectrometer.

The rim-driven plates are usually fitted closely but slidably between two other plates which have apertures comparable in size to the aperture 110.

Thus, with the variable-aperture device in place, the passageway for gas to enter the mass spectrometer may vary between a molecular leak and an aperture as big as the diameter of the sample container in the cell in the furnace, for example.

Leads 104, 106, sealed and extending though the tubular member 14, are used to power the device 102.

In operation, with the mass spectrometer pumped down by the diffusion pump 52 and with valves 40 and 54 closed, the cell probe 46 is inserted in the tubular element 42 between the closed valve 40 and the opened" compression fitting 44. The compression fitting is then tightened around the tube of the probe 46 and, after a sufficient reduction of pressure by means of the forepump 58, the valve 50 is closed and ball valve 40 and valve 62 are opened. The cell probe 46 is then slowly pushed through and past the compression fitting 44, past the valve 40 and into the bore in the furnace body inside of the helical winding 70. The heating coil 70 is energized at a controlled rate from a controller energization source (not shown) in coordination with the readings from control thermocouples in the sample cell probe assembly 46, as is known to those skilled in the art of differentialthermal analysis.

Because of the location of the furnace adjacent to the ion source 22, the material vaporized on heating of the sample material carried in the cell probe 46 is emitted into the ion source area of the mass spectrometer, where the vaporized material is ionized and analysis of the sample by mass spectrometer mean occurs simultaneously with the differential thermal analysis of the sample.

However, because some sample materials emit very substantial amounts of gas while they are undergoing differential thermal analysis, the tube I08 is often coupled to a vacuum system and the variable-aperture device 102 operated to reduce the opening from the furnace assembly into the mass spectrometer.

Alternatively, the tube 100 may be opened and a reactive gas or vapor (carbon dioxide or water vapor, for example) may be introduced to the area surrounding the end of a sample cell disposed in the furnace.

Thus, by suitable valving of the vacuum line 108 and suitable operation of the variable-aperture device 102, and possibly with the addition of gas or vapor through the line 100, it may be seen that the furnace assembly of this invention provides broad limits of use in differential thermal analysis work.

A cell probe assembly which is especially well adapted fur use with this invention is disclosed and claimed in Horst G. Langers copending application Ser. No. 840,28 l entitled, Differential Thermal Analysis Cell Assembly," filed July 9, 1969.

What is claimed is:

l. A furnace and sample insertion assembly for use under high-vacuum conditions, comprising thermal analysis cell insertion tubular means, a furnace assembly having sidewalls and ends disposed coaxially with respect to said tubular means and mechanically coupled and sealed at one end to said tubular means, said one end having a large aperture aligned with said tubular means, the other end of said furnace having variableaperture means coupled thereto to define a gas escape passage to a mass spectrometer, the ends and sidewalls of said furnace and said tubular means generally providing a gastight enclosure except for said gas escape passage, tubular passage means for withdrawing gases from said enclosure, and heating means disposed within said enclosure.

2. An assembly in accordance with claim 1, wherein tubular means are provided for introducing additional gas or vapor to said enclosure.

3. An assembly in accordance with claim I, wherein said variable-aperture means is controllable externally of the device on which said assembly is installed.

4. An assembly in accordance with claim I, wherein said heating means comprises a helical heating coil.

5. An assembly in accordance with claim 1, wherein the variable aperture of said variable-aperture means is disposed so as to be aligned with the sample material in a thermal analysis cell inserted in said assembly. 

1. A furnace and sample insertion assembly for use under highvacuum conditions, comprising thermal analysis cell insertion tubular means, a furnace assembly having sidewalls and ends disposed coaxially with respect to said tubular means and mechanically coupled and sealed at one end to said tubular means, said one end having a large aperture aligned with said tubular means, the other end of said furnace having variable-aperture means coupled thereto to define a gas escape passage to a mass spectrometer, the ends and sidewalls of said furnace and said tubular means generally providing a gastight enclosure except for said gas escape passage, tubular passage means fOr withdrawing gases from said enclosure, and heating means disposed within said enclosure.
 2. An assembly in accordance with claim 1, wherein tubular means are provided for introducing additional gas or vapor to said enclosure.
 3. An assembly in accordance with claim 1, wherein said variable-aperture means is controllable externally of the device on which said assembly is installed.
 4. An assembly in accordance with claim 1, wherein said heating means comprises a helical heating coil.
 5. An assembly in accordance with claim 1, wherein the variable aperture of said variable-aperture means is disposed so as to be aligned with the sample material in a thermal analysis cell inserted in said assembly. 